This invention relates to a pneumatic radial tire for a passenger car having an improved durability at a turnup portion of its carcass layer made of aromatic polyamide fiber cords.
Pneumatic radial tires for a passenger car generally use cords of organic fibers such as nylon fibers, polyester fibers, rayon fibers or the like as the cords of a carcass layer and include two or more belt layers having a structure in which steel cords of one layer cross those of the other layer or layers. Due to the existence of the belt layers, the pneumatic radial tires have improved wear resistance, high speed durability and maneuvering stability when compared with conventional bias tires. In addition, rolling resistance of the radial tires is reduced. In order to improve productivity and to reduce the tire weight, one-ply arrangement tends to be employed instead of two-ply arrangement for disposing the carcass layer.
In pneumatic radial tires having a tire size greater than 195/70 SR 14, however, it is difficult to employ the one-ply arrangement for the carcass layer by use of the organic fiber cords described above from the viewpoint of tire strength.
Therefore, it has lately been proposed to utilize aromatic polyamide fiber cords as the cords of the carcass layer of pneumatic radial tires as disclosed in Japanese patent application Kokai (laid-open) publication No. 49-120,303.
Aromatic polyamide fiber cords have by far higher strength than conventional organic fiber cords. Therefore, when aromatic polyamide fiber cords are used, the carcass layer which has heretofore required the two-ply arrangement can be formed by the one-ply arrangement so that productivity can be improved. However, since the aromatic polyamide fibers have high crystallinity due to their molecular structure, adhesion with covering rubber is low, and hence separation (peel of the cords from the rubber) is likely to occur at a turnup portion of the carcass layer when the aromatic polyamide fiber cords are used.